The present invention relates to a plate lock-up device mounted in a plate cylinder of a printing press to fix leading and trailing ends of a plate to be wound around the circumferential surface of the plate cylinder.
A gap having a substantially rectangular section is formed in the outer circumferential surface of a plate cylinder of each printing press so as to extend by almost the entire length of the plate cylinder. A plate lock-up device consisting of a leading plate lock-up unit for gripping the leading end, i.e., a gripper end, of the plate and a trailing plate lock-up unit for gripping the trailing end, i.e., an end opposite to the gripper end, of the plate cylinder is arranged in this gap and fixed on the bottom surface of the gap so as to extend in an axial direction of the cylinder.
Conventional leading and trailing plate lock-up units comprise elongated plate lock-up bases extending in the axial direction of a plate cylinder, a plurality of gripper plates pivotally supported by a plurality of bolts at edges of these plate lock-up bases and opened/closed upon pivoting to grip or release the plate with the plate lock-up plates, and a plurality of cams engaged with gaps of edges of the gripper plates. The plurality of cams are aligned along pivotal cam shafts. A plurality of compression coils springs are interposed between the plate lock-up bases and the gripper plates to bias the gripper plates in an open direction.
With the above structure, when a plate is to be gripped, the corresponding cam shaft is pivoted. Then, the gripper plates divided into a plurality of portions in the longitudinal direction of the plate cylinder are simultaneously released from engagement with the cams and are opened by an elastic force of the compression coil springs. The leading end of the plate is inserted between the gripper plates and the corresponding plate lock-up base, and the cam shaft is pivoted in a direction opposite to the direction described above. The gripper plates are pivoted and closed against the biasing forces of the compression coil springs by the action of the cams, thereby gripping the leading end of the plate.
The plate lock-up base of the trailing plate lock-up unit is supported on the bottom surface of the cylinder gap and is movable along the circumferential direction of the plate cylinder. A plurality of plate stretching bolts are threadably engaged at a plurality of positions in the longitudinal direction of this plate lock-up base such that the heads of the bolts abut against the wall surface of the gap of the plate cylinder.
With the above structure, after the leading end is gripped by the leading plate lock-up unit as described above is wound around the circumferential surface of the plate cylinder, the trailing end of the plate is gripped by the trailing plate lock-up unit. The plate lock-up bolts are tightened by circumferential movement of the trailing plate lock-up unit, and the plate is brought into tight contact on the circumferential surface of the plate cylinder. Spring members are inserted between the trailing plate lock-up unit and the gap. When the plate stretching bolts are loosened, the plate lock-up unit is moved toward the wall surface of the gap by the spring forces of the spring members and is loosened.
In such a conventional plate lock-up device, since a plurality of gripper plates are pivoted to pivot the cams so as to grip the plate, a gripping operation after adjustment of the gripper plates results in nonuniform gripping forces between the gripper plates. As a result, the plate tends to be deformed, and contact adjustment of the gripper plates is cumbersome to prolong the mounting time.
In the conventional plate lock-up device, as described above, since the plurality of plate stretching bolts are tightened to stretch the plate, it is difficult to uniformly stretch the plate, and mounting precision tends to be degraded. The plate stretching operation and the plate gripping operation must be performed at different work positions, resulting in cumbersome, time-consuming operations.